Humidity gauge problem

[Guest]

Hi,I've followed the procedure for testing our humidity gauge... and found that it's way off. It was at about 60% after a night in the jar with the salt & water.Two questions: how accurate is the above procedure and can anyone explain how it works to produce a 75% humidity environment in the jar? Third question: could too high humidity in our aquarium be related to the deaths of our first 3 hermies within 6-7 weeks of their arrival in our home? Two of them were molting (no ISO tank), but otherwise I can't think of any reason they died. I always kept the humidity at 75% according to our gauge, which means it was really much higher than 75.tia,cam

[Ren1216]

I dont think too high of humidity would kill them, it would more likey promote the growth of mold which Im sure is not healthy for the crabs... but, I dont think high humidity would be the reason for their deaths. Maybe someone more experienced can help you better with that question though.From what I have read, that guage calibrating test is accurate... but, I can not say from experience. Im starting to see that digital guages really are the way to go. They are more expensive, but the dial guages are really just a waste of money all together.

[NewCrabber]

Unless I read your post incorrectly, if you kept the humidity at 75%, according to the reading on the gauge, before you tested it and found it to actually be 60% RH after testing, then your humidity was not much higher than you thought at 75%, it was 15% lower. It would have had to be reading 90% for the humidity to be 75%. Even at six or seven weeks PPS could have been responsible for their deaths. Though, if the humidity was 60% much of that time, I would have to say it was probably a contributing factor. Almost all hermies come to us with some degree of stress and humidity being that low doesn't give them much of a chance to get past it. You don't say how far in their molts they got, but humidity plays a very important role in the success of molting. It has been reported that they are able to hold off the molting hormone if they are in less than desirable conditions, but I would imagine they can only do that for so long and who knows how long they'd been in bad conditions from the time of harvest. Take heart though. Crabbing is a learning experience for all of us and lessons we have all learned. The hard way for many of us, but certainly in this situation, it was through no fault of your own.The test is accurate, though I'm not able explain the chemistry of it all. But here is a snippet of an explanation..."For a calibration source, we're going to use salt - NaCl - plain table salt... Why salt? The following is a brief explanation of the chemistry, originally posted to asc by Peter Shenkin of Columbia University. Don't worry too much about the technical details - the point is that plain salt will, when used properly will maintain an exact 75% humidity in a sealed environment. A saturated solution at constant temperature & pressure has a fixed composition. [[ Explanation in terms of the Gibbs Phase Rule omitted. ]] Therefore, such a solution has a fixed vapor pressure. Thus, at constant temperature, no matter how much solid NaCl and how much water are present, the concentration of the NaCl in the water is fixed, just as long as both the solution and the solid phase are present. Therefore such a solution has a fixed vapor pressure. Now, it just happens to turn out that the vapor pressure of a saturated solution of NaCl in H20 is about 75% of the vapor pressure of pure water at any temperature close to room temperature. This means that at equilibrium, if there were nothing present except this solution and a vapor phase in contact with it (no air), the pressure above the solution would be about 15 mm_Hg, in round numbers, using 20 mm_Hg as the vapor pressure of water near room temperature, again in round numbers. As mentioned earlier, the only gas providing the pressure above the solution would be water vapor."I'm sure a more detailed explanation can be found on the web if you know what to look for, but if you're still interested and can't find anything, there is a site that sells cigars, humidors, etc., that says they will send one. They are just as concerned about humidity, if not more, than we are.

[Guest]

Thanks everybody for the hints!NewCrabber,Thanks *much* for the info about the NaCl and vapor pressure. It makes enough sense to satisfy me, but only because I just went through high school chemistry w/2 daughters this past year. I never could have figured it out myself. As far as my gauge goes, I think I'm correct in saying that I was keeping the tank too humid before now. If the humidity in the jar was 75% and my gauge read 60%, then when I put my gauge in the aquarium and it reads 75%, the humidity in my tank is really higher than 75. If that's not right, what am I missing? Now I should keep the gauge reading 60% (it can't be calibrated), right?Anyway, these new crabbies are oh-so-active after almost a week here. I remember how sluggish our first batch were the last few weeks before they died. They are all from the same store, so I'm assuming they are in similar health to start with. In grace,Cam

[NewCrabber]

Haha, you're not missing anything, I was, a little backward thinking there. I probably should stop posting in the middle of the night. You are correct, your gauge reads -15. I've not tried it, but if there is a screw on the back of your gauge, you should be able to calibrate it. Otherwise you'll have to go by the -15 reading.Anyway, welcome to LHC and I'm glad your new hermies are doing well.